Question

The correct order of reactivity of halogens with alkanes is :

• A. \( F_2 > Cl_2 > Br_2 > I_2 \)
• B. \( F_2 > Br_2 > Cl_2 > I_2 \)
• C. \( Cl_2 > F_2 > Br_2 > I_2 \)
• D. \( I_2 > Br_2 > Cl_2 > F_2 \)

Hint:

Reactivity of halogens decreases down the groupFluorine is most reactive while iodine is least reactive in free radical substitution reactions.

Answer 1

The Correct Option is A

Step 1: Understand halogenation of alkanes.
Halogenation of alkanes occurs via free radical substitution mechanism. The reactivity of halogens depends on bond dissociation energy and stability of radicals formed.

Step 2: Analyze reactivity trend.
Fluorine is the most reactive due to very low bond dissociation energy and highly exothermic reaction.
Chlorine is less reactive than fluorine but still highly reactive.
Bromine is moderately reactive due to higher bond energy and more selective behavior.
Iodine is least reactive because the reaction is endothermic and does not proceed easily.

Step 3: Arrange order.
Thus, the decreasing order of reactivity is:
\[ F_2 > Cl_2 > Br_2 > I_2 \]

Step 4: Conclusion.
Hence, the correct order is option (A).
\[ \boxed{F_2 > Cl_2 > Br_2 > I_2} \]